On Dec 14, 2005, at 6:00 PM, Ed Zavada wrote:

> 2) Changes to the protocol that break wire compatibility between  
> OpenPlay versions. For many people it wouldn't matter, for others  
> it would be a big deal. I can see several possible approaches:
> a. As you suggested, new version recognizes both versions and  
> either doesn't send ping or builds enum packet in such a way as to  
> let old OpenPlay be unaffected. This seems best if possible.
> b. Have a switch in the config that determines whether the ping  
> time is added to the packet or not, defaulting to off. This is  
> similar to Shawn's suggestion, but I think it's better than  
> separate API calls because it keeps the interface cleaner.

After looking into this, I think the only workable solution is going  
to be (b).

The problem is that if a new OpenPlay client is talking to an old  
OpenPlay server, there's no way to easily construct an enum query  
packet that'll work with both. The new enum query packet must contain  
the client's start time (so that it can determine the roundtrip time  
when the host passes it back in the enum response). The old parsing  
code is very rigid about the query packets it receives. Old hosts  
will reject any enum query that isn't an exact match for the old style.

One alternative is to send out 2 different enum query packets  
simultaneously in the new client code - an old-style one and a new  
one. However, you'll very likely get 2 queries back from each new  
host and then you've got all kinds of nasty decisions about what to  
do with the ping info that goes lost, or arrives later or whatever. I  
don't care for that, and it could only get worse in the future as  
enum query/response packets get updated for other features.

But (b) will do the trick. By adding a new optional field to the  
Config string, say "enumVersion=2", you can effectively say that your  
client will only send out new-style enum query packets and can only  
receive back query responses from hosts that recognize this version.  
An absence of this field in the config string (which is the case with  
the old OpenPlay code) would imply a version of 1 - the old style  
enum query/response. This should allow all the combinations of new/
old client/server OpenPlay to work. I'm not super-thrilled about this  
- it's a bit of an arcane way to tell OpenPlay that you want ping  
times, but c'est la vie.

I'll try to get this done soon, but my spare time is going to be  
limited until after the New Year, so it may be a few weeks.

--
Brad Oliver
bradman@pobo...

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